1. Field of the Invention.
The present invention relates to semiconductor electronic integrated circuits, and, more particularly, to integrated circuits made of III-V compound semiconductors including both two-terminal and three-terminal devices.
2. Description of the Related Art.
Communications, missile guidance, radar, and various other applications of microwave technology all would benefit from the lower cost of monolithic integration of components and subsystems. However, hybrid technology permits combinations of varying device types, circuits on varying substrate types, and passive components that are not entirely compatible with monolithic microwave integrated circuits (MMIC) technology. The best use of hybrid technology arises when high performance is required from a given circuit. In this case discrete devices (of possibly various types) are chosen and screened to insure maximum performance. passive circuits are produced on low loss substrates, and after devices are connected to the circuits some tuning is applied to obtain the maximum performance for the resulting hybrid arrangement.
Conversely, MMIC technology is currently based on the use of only one type of three-terminal device performing all of the circuits functions. The commonly used device type is the Schottky barrier gate GaAs field effect transistor (MESFET). The MESFET is flexible enough to be used in low noise amplifier, power amplifier, switch, mixer, doubler, and many other circuits. It performs most of these functions satisfactorily but none of them optimally. Further, a higher frequencies some of the system functions cannot be performed by three-terminal devices due to their inferior frequency response characteristics, and two-terminal devices must be employed.
The design and fabrication techniques for three-terminal and two-terminal types of devices are often different enough that the fabrication of circuits containing both types are only accomplished with multiple chips. Two-terminal devices such as mixers, IMPATT diodes, and Gunn diodes are normally produced in a way that the substrate becomes one of the terminals. A three-terminal device, such as a MESFET, is fabricated with all of its terminals on the top surface of a semi-insulating substrate. Furthermore, the epitaxial layer types and thicknesses for each type of device are sufficiently different from each other to preclude the growth of all layers in a single deposition run.
Chu et al, 28 IEEE Tr.Elec.Dev. 149 (1981) describe a 31 GHz receiver circuit where a regrowth technique was employed to deposit epitaxial layers suitable for mixers selectively on the surface; the remainder of the substrate was covered with MESFET material. This technique was later applied to the fabrication of a 35 GHz down converter: Chu et al, 1987 IEEE Microwave and Millimeter-Wave Monolithic Circuits Symposium, pp.63-67. In addition to the mixers and MESFETs, this circuit contained a Gunn diode serving as a local oscillator. Although operation of all components was demonstrated in separate chips, monolithic integration was not shown, and the proposed integration technique was again limited to the selective regrowth previously described. Regrowth, is a difficult technique and it is a problem of the known monolithic integration methods to provide simple and reliable processing.